THE HAGUE, Netherlands — In a cautious first step toward unlocking 30 years of tense relations, senior US diplomat Richard Holbrooke had a brief but cordial meeting with Iran’s deputy foreign minister yesterday at an international conference on Afghanistan.

The rare diplomatic approach was the first official face-to-face interplay between the Obama administration and the Iranian regime. Secretary of State Hillary Rodham Clinton cautioned that the brief talks between Holbrooke and Iranian diplomat Mehdi Akhundzadeh were cordial but not “substantive.”

“They agreed to stay in touch,” Clinton said at the close of a one-day conference on Afghan security and development that was designed partly to allow the diplomatic turn with Iran.

The meeting between Holbrooke, President Obama’s hand-picked Afghanistan envoy, and Akhundzadeh came on the sidelines of a session aimed at improving Afghanistan’s future prospects. Akhundzadeh pledged to help the reconstruction of its neighbor, but he criticized US plans to send more troops into Afghanistan.